As information era progresses, people can acquire a large amount of information, wherein information containing a user's opinion, sentiment inclination and the like may be generally referred to as opinion data. Businesses and advertisers and so on may use opinion data to assist decision making, for example, a decision on production, sales or advertisement investment for certain goods may be made in accordance with a users' inclination degrees towards the goods.
There are various text sources containing opinion data, wherein text sources are data sources convertible into text, such as thesis, investigation materials, blogs, microblogs and user's comments, as well as video, audio and images that may be converted into text for reading and the like. Furthermore, these opinion data are usually unstructured data. Therefore, it is difficult to make all-round statistics of the opinion data and use them to support decision making.